Liquidity Services (LQDT) taught a few good lessons in follow-on buying after its breakout last year. The goal of follow-on buying -- buying after a sound breakout from a base -- is to concentrate capital in your best stocks. The game plan: Begin an uptrend with positions in several, maybe a half-dozen, stocks. Then, as the bull run progresses, rotate the bulk of your portfolio into the one or two best performers. The first or second pullback to the